It is well known that complex electromechanical devices, such as computer disc drives, can be hanned by foreign substances which come into contact with vital components of the device. For example, dirt or dust particles which accumulate on the platters of a disc drive can damage the read/write head of the drive causing a "crash. " Thus, such devices are typically manufactured within a clean room environment and are sealed prior to leaving the clean room to reduce or prevent the possibility of such contamination.
However, the current breed of disc drives spin much faster and are more densely packed with data than prior drives. These speed and size increases require that the read/write heads fly very close to the surface of the disc platters (on the order of a micron). In light of these very low fly heights, it is possible for matter smaller than common dust or smoke particles to cause head/disc crashes. Indeed, even chemicals or chemical compounds which are outgassed by the disc drive may accumulate or be combined with other compounds to interfere with the drive heads.
Although some disc drive components outgas chemicals and chemical compounds while the drive is inactive, the level of outgassing typically increases when the drive is operating and the components are exposed to high temperatures. These outgassed chemicals and chemical compounds are easily transported throughout the drive (due to the rotation of the disc platters and the resulting air currents within the drive) where they typically bond to the substrate that coats the disc platters. In addition to physically interfering with the drive heads during operation of the drive, some outgassed compounds (e.g., adhesives) may react chemically with the drive heads during periods of inactivity when the heads are in direct contact with the disc platters. Such chemical reactions cause stiction between the heads and the disc platters which further contributes to early disc drive failure.
Thus, it is important for disc drive manufacturers to carefully monitor the outgassed compounds generated by the disc drive both in its static state,as well as during operation of the drive. The typical manner of determining the type and amount of compounds outgassed by a disc drive is to test the individual components of the disc drive. For example, each major component (or a portion thereof) may be tested by placing the component within a testing container and then sampling the interior volume of the container to determine which compounds have been outgassed during the course of the test. Such headspace sampling typically entails heating the sample container for a period of time and drawing a small sample from the sealed container. The sample is then analyzed with appropriate instrumentation, such as a gas chromatograph and a mass spectrum analyzer, to determine the composition of the outgassed compounds. Alternatively, dynamic sampling systems may be utilized in place of the above-described static sampling system to collect the compounds outgassed within the sample container. Dynamic sampling systems typically direct a flow of inert gas through the sample container and then through a trap which bonds with the outgassed compounds while allowing the inert gas to pass through the trap. One example of a dynamic system for sampling outgassed compounds from individual components is shown in U.S. Pat. No. 5,646,334 entitled MULTISAMPLE DYNAMIC HEADSPACE SAMPLER, issued Jul. 8, 1997 to Scheppers et al., assigned to the assignee of the present invention.
Once all of the individual disc drive components have been tested, the results may be combined and compared to a maximum or global tolerance for each identified compound. In this manner, individual disc drive components may be replaced or modified as necessary to maintain the overall outgassing levels of the disc drive below the defined maximum tolerances. However, the process of testing each disc drive component separately necessarily ignores interactions which may occur between the components as they operate together within the disc drive. Additionally, it is not possible to accurately test the contributions of some of the drive components outside of the drive itself. For example, the outgassing contributions of materials which are not fully exposed to the interior of the disc drive (e.g., pressure sensitive adhesives, gaskets, tape seals, etc.) are difficult to gauge from individual tests of those materials. Thus, individual component testing does not typically provide a true representation of the outgassing that occurs within the interior of an operative disc drive.
One solution to the problems associated with individual component testing is to pass an inert gas through the interior of the disc drive itself. Sampling the entire disc drive in this manner is typically accomplished by removing the drive top cover and replacing it with a modified cover having gas inlet and outlet ports formed therein. Gas inlet and outlet lines attached to the ports in the modified top cover then direct a flow of inert gas through the disc drive to remove any outgassed compounds for analysis. However, prior "whole drive" outgassing tests do not provide highly accurate or representative results due to the use of the modified top cover in place of the original drive top cover. For example, the modified top cover will not typically include all of the elements of a conventional top cover, such as breather filters, pressure sensitive adhesives, vibration dampeners or the original tape seal. Additionally, the original top cover typically contains absorbent filters for absorbing compounds outgassed within the disc drive. If the modified top cover does not contain these same filters then any outgassing test conducted with the modified top cover will detect unrealistically high levels of the outgassed compounds. Furthermore, the process of removing the original top cover and installing the modified top cover can lead to contamination and cause further anomalous readings.
While it is preferable to perform whole drive outgassing tests under actual operating conditions, the use of the above described modified top cover makes this process difficult, if not impossible. Because the top cover is an integral component of the disc-drive, the replacement of the original top cover with the modified top cover for the outgassing test frequently results in impaired operation or outright failure of the disc drive during the course of the test. Therefore, prior art whole drive outgassing tests are severely impaired due to the tendency of the modified top cover to both contaminate the test results and inhibit normal drive operation during the test.
In summary, regardless of whether individual disc drive components arc tested separately or the entire drive is tested with a modified top cover, prior outgassing tests have not provided truly representative or accurate indications of the compounds which are outgassed within a disc drive during operation of the drive.
It is with respect to these and other background considerations, limitations and problems that the present invention has evolved.